Plastics and glass are widely used in making optical elements, such as window panes, mirrors, spectacle lenses and goggles. During general use of these optical elements, due to changes in temperature and/or humidity of the surroundings, dewing may occur on the surfaces of the plastic or glass optical elements. This deteriorates the degree of transparency and thus, the visual performance provided by the glass or plastic optical elements.
To overcome such a problem, an anti-fogging film is generally coated on the surface of the optical elements on which dewing is expected to happen. Such an anti-fogging film and related techniques have been disclosed and discussed in a number of U.S. patents and one of the conventional ways used to form the anti-fogging film is to coat a polymer layer containing --C--OH functional group by means of immersion into a solution containing the high molecular compounds. Examples of such a technique include U.S. Pat. Nos. 4,242,412, 4,332,859 and 5,075,133.
There are also techniques of coating a compound film containing an ionic surface active agent of long chain molecules that contains --SO.sub.3 functional group and an inorganic salt by means of immersion, such as U.S. Pat. No. 4,214,908 which discloses a compound film containing an ionic surface active agent of long chain molecule that contains --SO.sub.3 functional group and an inorganic salt. The compound film is also formed by means of immersion technique.
Further, U.S. Pat. Nos. 4,778,909 and 5,134,021 disclose a technique of immersion into a coating forming solution(s) to form a single-layered or multiple-layered compound film containing polyvinyl alcohol, micro-particles of silica gel and organic silicon. The film so prepared generates --Si--OH functional groups in hydrolysis which possesses an excellent anti-fogging capability.
A significantly different technique is disclosed in U.S. Pat. No. 5,316,825 in which a single layer of specifically shaped micro-porous synthetic resin is provided for anti-fogging purpose.
Recently, Balzers Co., Swiss, develops a plasma polymerization technique for forming high molecular anti-fogging film containing --C.dbd.O or --C--OH functional group on optical lenses. The technique uses polyvinyl acetate monomer and oxygen as the reactants in forming the film. The detail of the technique may be obtained in Optical Engineering, September 1995, Vol. 34, page 2717.
The conventional ways of forming the anti-fogging film by immersion have the disadvantage of disposal of the immersion solution which may cause environmental problems. Further, the durability and stability of the antifogging films formed by means of previously discussed prior art techniques are far from ideal. As to the Balzers' technique, the film so obtained from the polyvinyl acetate monomer has problems in both hardness and adhesion.
It is thus desired to have a highly effective anti-fogging film having a simple structure but retaining the anti-fogging capability for a longer term.